A radiation detector for an imaging device typically comprises a semiconductor substrate with a pattern or array of conductive contacts on one surface of the substrate defining an arrangement of detector cells.
Various semiconductor materials can be used in radiation detectors. For example, for optical wavelengths and charged radiation (beta-rays), silicon has typically been used for the semiconductor substrate material, while cadmium zinc telluride (CdZnTe), cadmium telluride (CdTe), titanium bromide (TiBr), mercury iodide (HgI) and gallium nitride (GaN) can be used as substrate material in X-ray, gamma-ray and to a lesser extent beta-ray radiation imaging.
Such detector substrates need to be processed to produce a detector having a pattern of conductive contacts (e.g. pixel pads) on one surface, so that the detector may be position sensitive; that is, to ensure that the detector can produce a detector output indicating the position at which radiation impacts the detector. A readout chip then can be ‘flip-chip’ joined to the patterned side of the detector (e.g., by bump bonding using low temperature soldering with tin lead bismuth (PbSnBi) alloy solder or using balls of indium or conductive polymer material, gluing using conductive materials or other conductive adhesive layer techniques) so that the position dependent electrical signals which result from incidence and absorption in the detector cells of beta-rays, X-rays or gamma-rays for example, can be processed.
In some known radiation detectors, problems have been observed with certain characteristics of the conductive contacts. These include the conductive contacts having poor adhesion properties and shorter than desired life times. Shorter than desirable life times have been observed when radiation detectors are joined to a readout chip in a radiation imaging device, via a bump bonding technique using either a lead-based or a lead-free solder, for example.
It is therefore desirable to provide a method that produces radiation detectors with improved electrical properties.